Ram-type valve assemblies have long been employed in the past to control fluid flow, particularly in high pressure applications such as well blowouts and the like wherein it is necessary to effectively seal off the valve bore. Representative of such conventional valve asemblies are those depicted, for example, in Volume 1, page 978 and 980 of the "Composite Catalog of Oilfield Equipment and Services", 33rd Revision 1978-79, published by World Oil, and those depicted on page 8 and 9 of Instruction Manual No. 5/8505 entitled "Bowen Heavy Duty Blowout Preventers Hydraulic and Manual Types for Wireline and Tubing", 14th Printing, June 1979, published by Bowen Tools, Inc. In that the teachings and improvements of the present invention are particularly adaptable to the valve apparatus therein depicted and described, such disclosure is accordingly herein incorporated by reference with respect to the overall general construction and operation of such ram-type valve assemblies.
These valve assemblies frequently include two cylindrically shaped ram assemblies mounted in opposed relation and carried by a valve housing, said ram assembies having piston-shaped ram bodies being tranversely movable with respect to the bore of the housing and thus the fluid flow. Horizontally traversing the face of each ram body is a rectangular recess which is typically provided in the end portion of each ram assembly porximal to the bore. These recesses matingly receive generally rectangular block-shaped resilient sealing means having rectangular sealing faces extending slightly beyond the respective ram body face in the direction of the bore. Upon hydraulic or manual actuation of the valve assembly, the ram assemblies are caused to move inward toward the bore and one another until the aforesaid sealing faces are brought into sealing engagement with one another and with wire line, tubing, or the like (if any) disposed within the bore, so as to effectively seal the bore from further fluid flow.
The sealing means will often include metal upper and lower backup plates with a rectangularly shaped block of rubber sandwiched therebetween having the aforementioned sealing face oriented toward the bore. The thickness of the plates and rubber block are dimensioned so that the upper and lower plates are in sliding engagement along the center line of the ram assembly with respective horizontal upper and lower faces of the recess when the seal means is disposed therein.
Guide slots are provided on the outer surface of the lower plate running in the general direction of the ram assembly center line. These guide slots receive, in registry, respective tips of inner seal screws extending into the slots and carried by threaded vertical apertures within the body of the respective ram assembly.
It will thus be appreciated that relative movement of the seal means with respect to the ram body will be constrained by the length of the guide slots such that as either end of a slot contacts the tip of its respective inner seal screw disposed therein, further motion is prevented.
One serious problem associated with the design of such valve assemblies of the prior art concerns the hereinabove described manner in which the seal means are retained by the mating recess in the ram body, e.g., the guide slots and inner seal screws.
First, the inner seal screws are susceptible to working loose under vibrational and other adverse conditions often encountered, e.g., in oilfield applications, thus rendering the valve assembly inoperative. Moreover, and yet more serious, is the fact that the force behind the seal means exerted on the ram may, in some applications, exceed 15,000 lbs. Thus tremendous forces exerted between the screws and the backup plates often tend to shear the screws off. In either case, the loosened screws or sheared off portions thereof have been known to fall into the bore of the housing resulting in dangerous conditions even including, in some instances, total loss of control over oil wells and the like.
The disadvantages of the prior art including those hereinabove recited are overcome by the ram-type valve assembly apparatus of the present invention.